In preparation for removing the finalization step, simplify
incremental marking logic.

Change-Id: I929034e389edb0c9da78cd39fd497d5783aff7c4
Bug: v8:12775
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3704509Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81155}